[PSUBS-MAILIST] Thruster bladders

Wed Sep 15 17:56:37 EDT 2021

 Hi Rick, This is a home built brushless thruster. I have attached a photo of a pool test. It's not that clear but I have one tube coming off the motor that also contains the wiring. The tube is going to an oil compensator (big aluminium thing sitting in the plastic box). At a point along the tube I have a plummers T fitting where the wires are potted & come out from. Another tube is attached at 90 degrees & leads to the compensator. So I fill the motor up with 5cst silicone oil and don't worry about getting every bubble of air out. Then attach the hose & fill the rest of it from a fill port on the compensator. I have done away with that compensator and are using an air pressure regulator set at 5psi with a relieving valve set at 7-8 psi. The regulator has to be mounted upside down & have a hole in the handle area. The seawater comes in through the hole and compresses the air on to the regulator diaphragm, giving your set pressure of 5psi plus ambient water pressure. You could have a separate nipple on your motor for the air compensation tube. You fill the oil partially up the tube which acts as your oil level indicator. The beauty of having oil pressurised by air, is that if the oil leaked out the air will replace it & still keep the seawater out. BTW Karl Stanley has been to 2000ft with anair compensated system, using a 1st stage regulator that he has removed the spring from to give ambient pressure. I don't like the system where people wrap a tube around the motor & connect to two nipples. We discussed this at length & thought that the plastic tubing may not collapse to give ambient pressure till about 100psi. So you are basically relying on the motor seals. I can do you a dwg of how my system will be if you like! Alan

    On Thursday, September 16, 2021, 09:14:18 AM GMT+12, Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Hi Alan, You mentioned oil being flung up the feed tube and that it is clear and gives you an idea of the oil level. I am confused on how you have your feed tube set up? Does it come out of the top and back into the bottom of the can or is there only one hole in the can with a clear tube coming out a foot or so with a plug on the end and there must me air in the plastic tube to be able to give you an oil level and I didn't think you were supposed to have any air in the system at all?Rick
On Tue, Sep 14, 2021 at 6:35 PM Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Hi Rick, I am pressurising the oil in my thrusters with air at 5psi above ambient. Have found that without a bit of pressure the oil gets flung out of the motor housing & up the feed tube. The feed tube to the thruster is clear & gives me an indication of the oil level. I have spent a lot of time on the compensator issue, even 3d printing one & using a second stage regulator. I am currently ordering a stainless 316 pressure regulator with a 0-25psi output range and a stainless brewers over-pressure valve set at between 6-8psi. This is similar to what Brian Hughes is doing & a modification on what Cliff was using. Cliffs relieving type regulator couldn't cope with the back pressure build up. One advantage of going this route is that if you want to copy the Psubs electric manipulator (am working on my own version) you need to air compensate it & you can do both off this same unit. I am running a hose from the regulator to a manifold, from which hoses will go to 4 thrusters, the electric manipulator and over-pressure valve. Let me know if I can help. Alan

    On Wednesday, September 15, 2021, 04:14:32 PM GMT+12, Rick Patton via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 I am re thinking what to use for my oil expansion bladder. Would love to hear from everyone who chose to go with an oil filled thrusters on what they used and how they liked it. I remember someone saying that they used a squeeze ball gas tank primer which I like because it is small but I just spoke with someone who didn’t use a bladder and had never had a problem.
Rick 

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